As demand for portable apparatuses and communication apparatuses have increased sharply, there has been a strong necessity for a non-volatile memory which can overcome reading/writing limits of a volatile memory. For this, there has been suggested an MRAM using the fact that magnetic resistances are different according to relative arrangement of magnetic poles.
The MRAM is a memory for storing magnetic polarization in a magnetic material thin film. That is, the MRAM embodies a memory device by using a giant magneto resistive (GMR) or spin-polarized magneto-transmission (SPMT) phenomenon. In general, the MRAM uses a memory device using a magnetic phenomenon such as GMR and MTJ as a memory cell for storing data.
The MRAM using the GMR phenomenon takes advantage of the principle that resistance is larger when spin directions are different in two magnetic layers having a non-magnetic layer therebetween, than when spin directions are identical. The MRAM using the SPMT phenomenon takes advantage of the principle that larger current transmission is generated when spin directions are identical in two magnetic layers having an insulating layer therebetween than when spin directions are different.
FIG. 1 is a view illustrating a cell array and a sense amplifier of a conventional MRAM. Referring to FIG. 1, an MRAM cell includes word lines WL1–WLn, bit lines BL1–BLm, a sense amplifier SA and a data output buffer 2. A cell 1 is composed of a switching transistor T and a magneto-resistive tunneling junction (MTJ) element.
When a word line is selected, a current flows through the bit line. The amount of current is determined according to a magnetization direction of a variable magnetic layer of the MTJ element. The sense amplifier SA compares the current of the bit line with a reference signal REF to perform a sensing operation, and the data output buffer 2 transmits the data from the sense amplifier SA.
However, since the MTJ element is connected to the bit line, sensing sensitivity is reduced due to variations of a contact resistance in the stacked structure, thereby generating a mis-operation of the MRAM.